1. Field of the Invention
This invention relates to a valve, especially for internal combustion engines, in accordance with the preamble of Patent claim 1.
2. Disclosure Information
In engines in which fuel is not inducted via an intake manifold, or intake port, the valves disposed therein may coke very easily, which leads to a drastic deterioration in the performance and emission behavior.
The essential reason is that in engines with direct injection, unlike manifold injection engines, the inlet valves become considerably hotter, because the evaporative cooling of the fuel is absent. Small quantities of lubricating oil are always present on the valve stem, and these not only pass through the valve stem seal onto the valve stem during lubrication but are also passed via the crankcase breather system to the intake air in the form of oil mist and oil vapor and become deposited on the valve stem. In the case of engines with direct injection, unlike manifold injection engines, the lubricating oil is not washed off from the valve stem by the incoming fuel, so that in certain operating states of the engine the lubricating oil comes into contact with the hot valve cone, causes coking there and forms deposits that lead to loss of performance.
One solution to this problem is to cool the valve stem and valve cone sufficiently for the lubricating oil accumulating there not to cause coking.
A valve with liquid cooling is known from U.S. Pat. No. 4,169,488, in which the valve is designed to be hollow internally, with an internal second tube, whereby cooling liquid is passed through the valve stem to the valve cone and back. Such a valve is only suitable, however, for engines with very large valves, and, because such a valve is of complex construction, it is correspondingly elaborate and costly to produce.
U.S. Pat. No. 5,771,852 describes a valve having a hollow valve cone and valve stem, both of which are manufactured in one piece from a hollow tube. At the transition from the valve stem to the valve cone, elongate or curved indentations are disposed in the direction of the valve axis, these being intended first to increase the strength of the valve and secondly to cause swirling of the flow and hence improved removal of heat. A disadvantage here is that the introduction of heat into the valve cone through the valve disk is not prevented, and the valve cone thus undergoes a very high heat load, which is then only removed in the region of the indentations.
Accordingly, it is an object of the invention to design a valve such that it is simple to manufacture and remains cool in the region of the valve stem and the valve cone during operation, so that the lubricating oil present there does not cause coking.
This advantage is achieved, according to the invention, in that the valve disk has a lesser diameter than the recess in the valve cone, so that an insulation gap is formed between the recess in the valve cone and the valve disk edge.
The conduction of heat from the valve disk to the valve cone being interrupted by the insulation gap, the valve cone is subjected only to a fraction of the heat that would act upon it if there were a more rigorous connection to the valve disk, providing better conduction of heat. As the surface of the valve cone disposed directly in the combustion chamber represents only a narrow circle, the heat introduced into the valve cone via this surface can easily be removed via the valve seat.
The valve disk is exposed to the full heat load, because only small quantities of heat are removed via the structurally necessary contact with the valve cone. By a suitable choice of materials, both the heat resistance of the valve disk and the different heat expansion behavior of valve cone and valve disk can be adapted to the necessary operating conditions in the engine.
An advantageous embodiment of the valve envisages that a radially circumferential shoulder is disposed in the recess of the valve cone, on which shoulder the valve disk is supported in the direction of the valve axis. Such a shoulder is a practical way of passing into the valve seat, via the valve cone, the pressure forces arising as a result of the combustion pressure and acting on the valve disk. Such a shoulder also serves, during assembly of the valve, as a stop for the precisely axial positioning of the valve disk relative to the valve cone.
Advantageously, a plurality of shoulders distributed over the circumference are disposed in the recess of the valve cone, on which shoulders the valve disk is supported in the direction of the valve axis. This achieves the same functionality regarding force transmission and positioning as in the case of the circumferential shoulder, but the heat transmission is further reduced as a result of the smaller contact surface between valve disk and valve cone.
For the positive-fitting connection between valve cone and valve disk, the valve cone and valve disk comprise one or more joints at the circumference of the valve disk edge. In order to minimize the contact surfaces between valve cone and valve disk caused by the joints, and hence the heat transmission, the joints are disposed only in certain sections at the circumference of the valve disk edge. The joints may be produced by calking, welding or crimping onto the valve cone. Other joints are also possible, provided that the requirements in terms of strength and low heat transmission are met.
A further advantageous embodiment envisages that radial centering cams are disposed at the valve disk edge. These serve to center the valve disk in the recess during assembly. As a result of the centering, a constant insulation gap is ensured over the entire circumference of the valve disk edge.
A further embodiment envisages that radial centering cams are disposed in the recess of the valve cone. They perform the same function there as when disposed at the valve disk edge. A further advantage is that in the case of calking of valve cone and valve disk, these cams can simultaneously be used as calking material.